Dipole interaction, adhesion

As previously mentioned, electrodynamic interactions, such as those arising from London forces, can also contribute to the adhesion of particles. These forces are dominated by dipole interactions and are broadly lumped into the classification known as van der Waals interactions. A more detailed description of van der Waals interactions than can be presented in this article is given in books by Israelachvili [95] and by Rimai and Quesnel [96]. 

Adhesive—A substance capable of holding materials together by surface attachment through forces such as dipole-dipole interactions. 

Rubber as the Disperse Phase. In polyblend systems, a rubber is masticated mechanically with a polymer or dissolved in a polymer solution. At the conclusion of blending, a rubber is dispersed in a resin as particles of spherical or irregular shape. We can further subdivide this system into three classes according to the major intermolecular forces governing adhesion (a) by dispersion forces—e.g., the polyblend of two incompatible polymers, (b) by dipole interaction—e.g., the polyblend of polyvinyl chloride and an acrylonitrile rubber (56), and (c) by covalent bond—e.g., an epoxy resin reinforced with an acid-containing elastomer reported by McGarry (43). 

To understand the reasons for different predictions of different methods, Li et al. [83] measured the adhesion between a variety of polymers with well-controlled backbone chemistry These polymers include poly (4-methyl 1-pentene) [TPX], poly(vinyl cyclohexane) [PVCH], polystyrene [PS], poly(methyl methacrylate) [PMMA], and poly(2-vinyl pyridine) [PVP], poly(4-tert-butyl styrene) [PtBS], poly(acrylonitrile) [PAN], poly(p-phenyl styrene) [PPPS], poly(vinyl benzyl chloride) [PVCB]. It may be noted that, among the polymers listed above, TPX and PVCH are purely dispersive in nature. PS is predominantly dispersive with some dipole-induced dipole interactions. 

No comprehensive theory exists for predicting interlayer adhesion in coextrusion (see Adhesion). Most knowledge comes from trial-and-error testing that has led to qualitative rating charts for polymer adhesion such as the one shown in Table 3. Polymer or copolymer fiinctionality plays a strong role. Polar polymers tend to adhere to each other adhesion is difficult between nonpolar polsrmers. Some polymers form covalent bonds in addition to H-bonding, acid-base, ionic, and dipole-dipole interactions (75-78). 

The main forces responsible for adhesion are van der Waals, which for convenience are considered to be made of three main contributions Dipole-dipole interaction (Keesom force), dipole-induced-dipole interaction (Debye force) and London dispersion force. A hydrogen-bonding force can also be induded in the interaction. 

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